This invention relates to low fusing high-expansion dental porcelain especially useful for the fabrication of both all-ceramic and porcelain-fused-to-metal (PFM) restorations.
Porcelains are typically designed to be used in the manufacture of either all-ceramic dental restorations or in PFM restorations, but are not normally functional with both types of restorations due to the differences in properties of ceramics and metals. One such porcelain, OPC(copyright) Low Wear(trademark) porcelain, available from Jeneric/Pentron Inc., Wallingford, Conn. and covered in copending, commonly assigned patent application Ser. No. 09/133,582 filed Aug. 13, 1998, now U.S. Pat. No. 6,120,591, which is hereby incorporated by reference, was initially designed to be used as overlay for pressed all-ceramic restorations as well as for the fabrication of porcelain jacket crowns and veneers. However, OPC(copyright) Low Wear(trademark) porcelain is not currently used for PFM restorations despite its wear resistance, forgiveness to natural dentition and strength being superior to those of conventional PFM porcelains as shown in the Table 1 below:
The major obstacle preventing use of the OPC(copyright) Low Wear(trademark) porcelain in PFM restorations is the absence of an opaque/alloy combination compatible with this porcelain having relatively high expansion of about 17xc3x9710xe2x88x926/xc2x0 C. (25xc2x0 C.-500xc2x0 C.).
There exists a Golden Gate System(trademark) for PFM restorations available through Degussa(trademark) (Dental Division, South Plainfield, N.J.) which combines Duceragold(trademark) porcelain and Degunorn(trademark), type IV crown and bridge alloy (CTE=16.4xc3x9710xe2x88x926/xc2x0 C., 25xc2x0 C.-500xc2x0 C.). This system requires rather tedious multistep alloy preparation procedures including a necessary wash bake step prior to application of the opaque; and an excessively long (16-20 min) and complex first dentine bake to assure proper bonding and compatibility of the Duceragold(trademark) porcelain to the Degunorm(trademark) alloy. In particular, the cooling segment (3-4 min between 720xc2x0 C. and 680xc2x0 C.) in the first dentine bake is required by the manufacturer to grow additional leucite and may be an indication of instability of leucite in this porcelain. The following Table 2 below sets forth the various properties of the Duceragold(trademark) porcelain.
U.S. Pat. No. 5,453,290 to Van der Zel is directed to a dental porcelain for use with a dental alloy. The porcelain described therein must be fabricated from three frits, making it more difficult and costly to control the expansion and the glass transition temperature of the final product. Moreover, the CTE of the porcelain must be below the CTE of the alloy by 0.5-1.5 limiting the components to be used together. There is a need to provide a porcelain-fused-to-metal system for dental restorations having simple manufacturing procedures. It is desirable to provide a porcelain that is compatible with alloys of relatively high expansion. It is desireable to provide a two-frit porcelain for use in PFM restorations.
These and other objects and advantages are accomplished by opaque porcelains for use with metal cores in the manufacture of PFM restorations. The porcelains exhibit a coefficient of thermal expansion (CTE) substantially equal to or slightly above the CTE of the metal to which it is applied. In a preferred embodiment, the porcelains exhibit a CTE equal to or up to about 1.0xc3x9710xe2x88x926/xc2x0 C. higher than the dental alloys to which they are applied as the opaque. The porcelains are fabricated from a mixture of two frit compositions. A high expansion, leucite containing frit is combined with a low fusing glass frit to provide a porcelain having an expansion in the range of 16.9 to about 18.5xc3x9710xe2x88x926/xc2x0 C. in the temperature range of 25xc2x0-600xc2x0 C. By combining two frits, the expansion and fusing temperature can be controlled to the values stated above.